A traditional method for providing shielding between a crossover of a RF line and a DC/control line involves providing the DC/control line as a coaxial cable. The coaxial cable provides the necessary electromagnetic shielding so that an RF signal carried on a RF microstrip line is unperturbed by a DC/control signal on the DC/control line. The use of a coaxial cable for the DC/control line is unfeasible or impractical in a large number of applications, however.
An important application where the use of coaxial cable for the DC/control line is not suitable is in a multilayer board environment. The traditional method for providing isolation between crossing of RF and DC/control lines in such an environment entails using an intermediate ground plane layer in the multilayer board array. The ground plane layer is positioned between the RF and DC layers. This approach, however, requires three metallization layers: one for the RF transmission line metal, one for the ground plane layer, and one for the DC/control line metal. The use of three metalization layers is more costly in terms of material and fabrication than a two-layer design (one layer for the RF line and one layer for the DC/control line).
Thus, what is needed is a practical, economical method for providing isolation between crossing of RF and DC/control traces without the need for bulky and expensive shields or additional metalization layers.